Comparative approaches provide unique experimental models and a perspective of biological history of regulation of blood pressure. Therefore, knowledge obtained from studying lower animal forms should be very applicable towards the understanding of the blood pressure control system in man. The aim of the project is to determine evolutionary trends in the role of the renin-angiotensin system (RAS) and adrenergic nervous system in control of blood pressure. The major findings during the first year are as follows: 1) In the bony fish (eel) and bird (chicken), the amino acids in positions 1 and 8 of angiotensin are important for receptor binding and action, and a considerable portion of angiotensin's pressor effect appears to be mediated by catecholamine release. 2) Isoproterenol (beta-adrenergic drug), but not norepinephrine (alpha-adrenergic drug), increased plasma renin activity (PRA) in the aglomerular toadfish with a concomitant decrease in blood pressure (BP), and propranolol abolished both effects. 3) Many bird species demonstrate genetically elevated BP. Mean aortic pressure of the conscious chicken was 145 plus or minus 3 mm Hg, and the heart rate was 300 plus or minus 5 beats/min. Daily injection of propranolol (beta-adrenergic blocking drug) considerably decreased BP and heart rate, whereas PRA remained the same, suggesting that beta-adrenergic function may be involved in BP regulation in the bird. We plan to further determine: 1) interactions among angiotensin, the adrenergic nervous system, and prostaglandins by using in situ vascular bed preparations in the chicken; 2) the role of sodium balance in the RAS and blood pressure in the conscious chicken; and 3) the chemical evolution of angiotensin and structure-activity relationship in primitive fishes.